The present invention relates generally to an apparatus for energy conversion and, in particular, to a wind-powered electrical generator.
In the past, the windmill has been the primary means for converting wind energy into useful work. It is notable that since the 14th Century when the windmill came into use, there has not been any significant intrinsic principal change in its construction. While the old watermill wheel has been transformed into the hydro-electric turbine, the windmill has remained the same, except that it has been built larger and at an increasingly prohibitive cost.
In recent years concentrating tubes have been used to gather the wind stream entering a large surface area and to direct such wind stream into a progressively narrowing passageway, thereby concentrating the force of the wind stream. Typical of such efforts are Murphy, U.S. Pat. No. 4,127,356 entitled "Wind Motor Machine" and D. R. Oliver, U.S. Pat. No. 1,783,669 entitled "Air Motor."
In Murphy, a horn-shaped structure is used to concentrate the incident wind stream which is thereafter directed to flow over an impeller. The impeller rotates a shaft which is coupled to an electric generator. In Oliver, a conically-shaped structure is used to concentrate the wind stream. The concentrated wind stream is directed into and through an elongated tube in which are mounted a number of turbines. These turbines are mounted on a shaft and coaxially with the tube. The shaft, in turn, is attached to an electric generator. In both Oliver and Murphy, the structures are mounted on a rotatable turntable so that the concentrating structures can be orientated into the wind stream flow.
Among the disadvantages associated with the above wind generator configurations are size and efficiency. In order to accommodate the multiple turbine blades and the flow-through design in Oliver, the tube which contained the blades and the shaft comprises at least 50% of the total length of the wind generator. In Murphy, the turbine wheel extends beyond the confines of the concentrator structure.
In Oliver, the electric generator is indirectly coupled to the shaft, as necessitated by the large size of the structure. This indirect coupling gives rise to the need for additonal belts and wheels in order that the coupling may be implemented. In Murphy, the turbine is contained partly within the concentrator structure and partly outside of the concentrator structure. As such, the turbine is used much like a water wheel, wherein a fraction of the available blade surface is used to convert the wind stream into rotational motion. As a result, the efficiency of the conversion is reduced and the minimum wind speed required for operation of the turbine is increased.
Another disadvantage is believed to exist in the Murphy and Oliver configurations; that is, a susceptibility to wind gusts. In both the design and operation of wind powered generators the variability of the wind is a significant factor. The turbines in each are directly exposed to the full force of the incident windstreams. Thus, the turbines should be capable of operation over a highly variable wind speed range, and the generators, which convert the rotational energy supplied by the turbines into electricity, should be capable of operating over a wide range of rotational velocities.
In order to permit operation over highly variable wind speeds, the efficiency of the generator is often sacrificed. Additionally, the above turbine and generator should be designed to withstand peak gusts, which can have velocities which are very large. This often results in the use of turbines and generators which are over-designed with respect to the average operating conditions of the wind powered installation.
In the present invention, a focusing surface is used in conjunction with a concentrator structure, thereby permitting the turbine to be included wholly within the concentrator structure, and acting to reduce the effects of wind gusts on the turbine and associated generators. This, in turn, results in size reduction, as well as increased conversion efficiency.